Before your food passes from the mouth and down your esophagus, salivary amylase, an enzyme in saliva, begins to digest the starch in your bread. That is the start of chemical digestion. ... The passage of the bolus through the esophagus to the stomach occurs by peristalsis, a series of wave-like muscle contractions.
Answer:
First, you chew the bread in your mouth which contains complex carbohydrates like starch and cellulose. In your mouth, your salivary glands are specialised cells in glands to produce a carbohydrase enzyme like amylase in your saliva. Amylase partially breaks down carbohydrates like starch which is a big food molecule that cannot be digested. It breaks down into a smaller molecule that can be digested into maltose. This is carried out by a process like the lock and key theory. The enzyme, amylase has an active site where the substrate, in this case being the carbohydrate, binds to the enzyme because it fits the certain shape. The reaction then takes place rapidly as the substrate is catalysed. Products are released from the surface of the enzyme because it breaks up the large molecule into smaller ones and the enzyme is ready to be used again.
The partially broken up food then travels down your gullet and into the stomach where it's lined with millions of glands that produce the enzyme, pepsin and hydrochloric acid. The right pH levels are needed for the enzymes to work best in like pepsin (pepsin breaks down proteins and not carbohydrates) but hydrochloric acid kills bacteria in the food.
Some enzymes that catalyse digestion are made in the pancreas, like amylase. The pancreas secretes the digestive juices onto the food which breaks it down further. Depending on the size and type of meal, the food then leaves your stomach and moves onto the small intestine. As it moves into the small intestine, bile (which is produced in the liver) is squirted onto the food through the bile duct. The bile neutralises the acid that was added to the food by the stomach. This provides the alkaline conditions necessary for the enzymes in the small intestine to work most effectively.
The food then travels through the small intestine where amylase further breaks down the food molecules into smaller, soluble ones which can be absorbed into your bloodstream. The small intestine is adapted to have a very large surface area and is covered in villi. Villi are adapted to have large surface area and are only one cell thick so nutrients only have a short distance to diffuse into the blood. It also has a good blood supply to the blood vessels. This greatly increases diffusion and active transport from the small intestine to the blood.
Finally the muscular walls of the small intestine squeeze the undigested food into the large intestine. water is absorbed from the undigested food into your blood. The material left forms the faeces. Faeces are stored and then pass out of your body through the rectum and anus back into the environment.
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